Method of making a semiconductor device with embedded stressor

ABSTRACT

A method for forming a semiconductor device includes providing a semiconductor substrate; forming a gate dielectric over the semiconductor substrate; forming a gate electrode over the gate dielectric; forming an insulating layer over a sidewall of the gate electrode; defining source and drain regions in the semiconductor substrate adjacent to the insulating layer; implanting a dopant in the source and drain regions of the semiconductor substrate to form doped source and drain regions; forming a sidewall spacer adjacent to the insulating layer; forming a recess in the semiconductor substrate in the source and drain regions, wherein the recess extends directly underneath the spacer a predetermined distance from a channel regions; and forming a stressor material in the recess. The method allows the stressor material to be formed closer to a channel region, thus improving carrier mobility in the channel while not degrading short channel effects.

BACKGROUND

1. Field

This disclosure relates generally to semiconductor devices, and morespecifically, to semiconductor devices with embedded stressors.

2. Related Art

Embedded stressors have been found to be effective in increasingtransistor performance by increasing carrier mobility. The typicalprocess includes forming recesses in the source/drain regions and thenfilling the recesses with a semiconductor material that acts as astressor to provide stress to the channel while also being effective asa source/drain. For the channel being silicon, the use of silicongermanium stressors has been found to be effective for the P channeltransistors and silicon carbon has been found to be effective for Nchannel transistors. To increase stress and thereby increase transistorperformance, the stressors are desirable adjacent to the channel. Thus abenefit of the stressors being immediately adjacent to the channel ismaximizing the stress to the channel. The cost of this benefit can beincreased leakage due to loss of short channel control if the stressorscontinue straight down from the lateral edge of the channel. Thus, abenefit is seen in attempting to provide a stressor that is shallow inthe area immediately adjacent to the channel to and is deep in the areawhere the source/drain contact is formed. This then brings the stressoradjacent to the channel to increase transistor performance while notdegrading current leakage. This can be achievable but has been found toadd processing complexity.

Accordingly there is a need to achieve the benefits of embeddedstressors while avoiding or reducing the problems associated with makingthem.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited by the accompanying figures, in which like references indicatesimilar elements. Elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale.

FIG. 1 is a cross section of a semiconductor device at a stage inprocessing according to one embodiment;

FIG. 2 is a cross section of the semiconductor device of FIG. 1 at asubsequent stage in processing;

FIG. 3 is a cross section of the semiconductor device of FIG. 2 at asubsequent stage in processing;

FIG. 4 is a cross section of the semiconductor device of FIG. 3 at asubsequent stage in processing;

FIG. 5 is a cross section of the semiconductor device of FIG. 4 at asubsequent stage in processing;

FIG. 6 is a cross section of the semiconductor device of FIG. 5 at asubsequent stage in processing; and

FIG. 7 is a cross section of the semiconductor device of FIG. 6 at asubsequent stage in processing.

DETAILED DESCRIPTION

In one aspect, a source/drain and extension region is formed byimplanting into a semiconductor layer using a gate and an offset spaceras a mask. The implant has the affect of altering the etchcharacteristic of the portion of the semiconductor that receives theimplant. The result is that the source/drain and extension region has adifferent etch characteristic from the semiconductor layer in which itis formed. A sidewall spacer is formed around the gate. A source/draincontact region is recessed with a first etchant using the sidewallspacer as a mask. The source/drain extension region is recessed using asecond etchant that etches the extension region selectively over thesemiconductor layer due to the different doping concentrations in thetwo regions. The second etch thus leaves a recess under the sidewallspacer. The recess is then filled with a stressor. This also partiallyfills the recess of the source/drain region. The recess is thencompletely filled with stressor material that can be of a differentin-situ doping concentration from what filled the source/drain extensionregion. This is better understood by reference to the drawings and thefollowing description.

Shown in FIG. 1 is a semiconductor device 10 comprising a substrate 12,an insulating layer 14 over substrate 12, a semiconductor layer 16 overinsulating layer 14, a gate dielectric 18 over a portion ofsemiconductor layer 16, gate electrode 20 over gate dielectric 18, aninsulating layer 24 over gate electrode 20, a sidewall spacer 22 aroundgate electrode 20, and source/drain and extension regions 28 and 30 insemiconductor layer 16 formed by an implant 26 using gate electrode 20as a mask. Substrate 12 is for providing physical support forsemiconductor device 10 and may be silicon. Insulating layer 14 providesinsulation between substrate 12 and semiconductor layer 16 and may besilicon oxide. Semiconductor layer 16 is for use in forming transistorsand potentially other devices and may be silicon. Substrate 12,insulating layer 14, and semiconductor layer 16 together form asemiconductor-on-insulator (SOI) substrate. A bulk substrate may be usedinstead. Gate dielectric 18 is very thin, such as 20 Angstroms, comparedto all of the other layers and may be silicon oxide. Gate electrode canbe doped polysilicon but could be a stack of materials, especially oneor more metal layers and may or may not further include polysilicon.Insulating layer 24 may be silicon nitride. Sidewall spacer 22, whichmay be silicon oxide or silicon nitride, is relatively thin for asidewall spacer, about 100 Angstroms, and is for protecting the sidewallof gate electrode 20 and providing a small offset of the source/drainand extensions 28 and 30 from the edge of gate electrode 20. Implant 26can be a conventional source/drain extension implant using arsenic forthe case of an N channel transistor. Implant 26, in this case, is forchanging the etch characteristic for source/drain and extension regions28 and 30 from that of semiconductor layer 16. That a conventionalsource/drain extension implant can be used to achieve this is a benefitin that standard processing can be used. In this example ofsemiconductor layer 16 being silicon, arsenic doping changes the etchcharacteristic so that arsenic-doped silicon, with the properly selectedetchant, can be etched selective to silicon that has not been arsenicdoped. Source/drain extensions 28 and 30 are only doped to a depth ofabout a third of the width of gate electrode 20 which corresponds to thechannel length but can be adjusted to optimize the extension recessdepth.

Shown in FIG. 2 is semiconductor device 10 after forming an insulatinglayer 32 over gate electrode 20 and source/drain extension regions 26and 28. In a typical integrated circuit, transistor of both P and N typewould be formed. This example is for N-type but is applicable to Pchannel transistors as well. Insulating layer 32 would be formed overthe P channel transistors as well as shown for the N channel transistor.

Shown in FIG. 3 is semiconductor device 10 after forming a sidewallspacer 34 around gate electrode 20. Sidewall spacer 34, at the widestpoint, is about the same as the width of gate electrode 20 but can bethicker or thinner to adjust the final length of a stressor yet to beformed in the source/drain extension portion of regions 28 and 30.Sidewall spacer may be silicon nitride.

Shown in FIG. 4 is semiconductor device 10 after removing insulatinglayer 32 in the areas not covered by sidewall spacer 34. For the othertype of transistors, which are not shown, insulating layer 32 would notbe removed.

Shown in FIG. 5 is semiconductor device 10 after etching semiconductorlayer 16 using sidewall spacer 34 and insulating layer 24 as a mask toleave a recess 36 for one source/drain contact region and a recess 38for another source/drain contact region on an opposing side of gateelectrode 20 from that of recess 36. An effective etchant for etchingthrough arsenic-doped silicon and undoped silicon is sulfur hexafluoridewith parameters that cause the etch to be anisotropic. For this exampleof sulfur hexafluoride, the etch is a dry plasma etch using a biassource. Other anisotropic etches may also be used. Nitrogen trifluoridein the presence of chlorine is one example. Another example is hydrogenbromide in the presence of chlorine. Oxygen may also be an effectivecomponent of the etch chemistry. In this case undoped silicon means adoping level below 1 e 18 (one times ten to the eighteenth) atoms percubic centimeter. Doped means in excess of a doping level of greaterthan 1 e 19 atoms per cubic centimeter. Carrier gases include argon andhelium and others may also be effective. It is preferable that thedifference between doped and undoped concentrations be at least a factorof about one hundred. Remaining portions of source/drain extensionregions 28 and 30 remain under sidewall spacer 34.

Shown in FIG. 6 is semiconductor device 10 after changing the etchconditions to remove the remaining portions of source/drain extensionregions 28 and 30 to leave recesses 40 and 42, respectively. Disablingthe bias source is effective in converting the etch to an isotropicetch. With the etch being isotropic, the remaining portions ofsource/drain extension regions 28 and 30 etch much faster thansemiconductor layer 16. This etch can be more tightly controlled and theselectivity can be somewhat tuned by controlling the concentration ofthe sulfur hexafluoride. Thus the selective etch of the remainingportions of source/drain extension regions 28 and 30 can be achievedwith a change in etch conditions of turning off the bias power anddiluting the sulfur hexafluoride with an increase in the inert carriergas. The etch that forms recesses 36 and 38 is different than the etchthat forms recesses 40 and 42 but it can also be viewed as a continuousetch because the two different conditions for the two etches do notrequire any delay or removal of semiconductor device 10 from the etchchamber. Even a change in the active reactant may not require any delayin the etching. Such a change may not require a change in the etchequipment.

An alternative is for the second etch to be performed in a tool in whichepitaxial growth can be performed. This can be done with minimal change,if any, to currently available equipment because the second etch doesnot require a bias power. Thus, the isotropic etch can be performed in achamber that is also capable of performing epitaxial growth. In suchcase, the subsequent epitaxial growth can be done in situ following thesecond etch.

Shown in FIG. 7 is semiconductor device 10 after epitaxially growingsource/drain region 44 in recesses 36 and 40 and source/drain region 46in recesses 42 and 46. Source/drain regions 44 and 46 also are stressorsthat are, for this described case of N-type, formed from silicon carbonthat are in situ doped with phosphorus in that they are doped as theyare grown. Being silicon carbon, they provide a tensile stress to thechannel, the region between source/drain regions 44 and 46 immediatelyunder gate 20. Semiconductor device 10 of FIG. 7 is a functionaltransistor. Subsequent processing would typically include silicidingsource/drain regions 44 and 46 and forming overlying interconnectlayers. Other fills for different stresses can be silicon germanium(SiGe) or even silicon, germanium, and carbon (SiGeC).

As an option, the phosphorus doping concentration of source/drainregions 44 and 46 can be changed after the extension recesses 40 and 42have been filled. In such case the region of recesses 40 and 42 can havea doping concentration selected for the purpose of being source/drainextensions and the region for making contact to source/drain regions 44and 46 can have a doping concentration selected for the purpose ofsiliciding and making electrical contact. This staged doping is alsoapplicable for the reverse case of forming a P channel transistor withsilicon germanium stressors that are compressive as source/drain regions44 and 46. In the case of P channel transistors, source/drain regions 44and 46 would be in situ boron doped instead of phosphorus. Also for theN channel case, arsenic may be used as the dopant.

The resulting structure, which requires minimal increased processingcomplexity, has the desired stressor immediately adjacent to the channelbut spaced back at the lower depth. Thus, the current leakage issuesthat arise from the source/drain being to close at the lower depths doesnot arise.

By now it should be appreciated that there has been provided a methodfor forming a semiconductor device that includes providing asemiconductor substrate, forming a gate dielectric, forming a gateelectrode, forming an insulating layer, defining source and drainregions, implanting a dopant, forming a sidewall spacer, forming arecess, and forming a stressor material. The gate dielectric is formedover the semiconductor substrate. The gate electrode is over the gatedielectric. The insulating layer is over the sidewall of the gateelectrode. The source and drain regions are in the semiconductorsubstrate adjacent to the insulating layer. The dopant is in the sourceand drain regions of the semiconductor substrate to form doped sourceand drain regions. The sidewall spacer is adjacent to the insulatinglayer. The recess is in the semiconductor substrate in the source anddrain regions. The recess extends directly underneath the spacer apredetermined distance from a channel region. The stressor material isin the recess. The implanting the dopant in the source and drain regionsmay further comprise implanting one of arsenic, phosphorus, boron,oxygen, carbon, nitrogen, or boron difluoride in the source and drainregions. The forming the recess in the semiconductor substrate mayfurther comprise isotropically etching the doped source and drainregions. The forming the stressor material in the recess may furthercomprise epitaxially growing silicon carbon (SiC), silicon germanium(SiGe), or a combination of silicon, carbon, or germanium (SiGeC) in therecess. The forming the stressor material in the recess may comprisegrowing a first stressor layer in the recess and growing a secondstressor layer over the first stressor layer. The forming the recess mayfurther comprises performing first and second etch processes. The firstetch process removes a first portion of the recess adjacent to thesidewall spacer. The second etch process removes a second portion of therecess directly underneath the sidewall spacer. The second etch processmay be performed in-situ with forming the stressor material. The secondetch process may be performed using process gases selected from a groupcomprising HBr, SF₆, NF₃, Cl₂, O2, Ar, and He. A thickness of theinsulating layer may determine the predetermined distance. The formingthe stressor material may further comprise providing one of either atensile stress or a compressive stress on the channel region of thesemiconductor device. The forming the stressor material in the recessmay comprise growing first and second stressor layers. The firststressor layer is formed with a first in-situ doping concentration inthe recess. The second stressor layer is formed with a second in-situdoping concentration over the first stressor layer. The forming astressor material may further comprise growing the stressor material onexposed silicon in the recess. The forming a stressor material mayfurther comprise growing the stressor material over the semiconductordevice, selectively etching the stressor material from the gateelectrode and the spacer, and repeating the growing and etching apredetermined number of times.

Also there is described a method for forming a semiconductor device. Asemiconductor substrate is provided. A gate dielectric is formed overthe semiconductor substrate. A gate electrode is formed over the gatedielectric. A capping layer is formed over the gate electrode. An offsetspacer is formed over a sidewall of the gate electrode and the cappinglayer. A dopant in source and drain regions of the semiconductorsubstrate is implanted adjacent to the offset spacer to form dopedsource and drain regions. A sidewall spacer is formed adjacent to theoffset spacer. A recess is formed in the semiconductor substrate in thesource and drain regions. The recess extends directly underneath thesidewall spacer a predetermined distance from a channel region, thepredetermined distance determined by a thickness of the offset spacer. Astressor material is formed in the recess. The forming the stressormaterial may further comprise forming one of either a first stressormaterial or a second stressor material in the recess, the first stressormaterial comprising silicon carbon (SiC) for providing tensile stressfor the channel region being of an N-channel transistor, and the secondstressor material comprising silicon germanium (SiGe) for providingcompressive stress for the channel region being of a P-channeltransistor. The forming the recess may further comprise performing afirst etch process to remove a first portion of the recess adjacent tothe sidewall spacer and performing a second etch process to remove asecond portion of the recess directly underneath the sidewall spacer.The second etch may be performed in-situ with forming the stressormaterial. The second etch may be performed using process gases selectedfrom a group comprising HBr, SF₆, NF₃, Cl₂, O₂, Ar, and He.

Yet also described is a method for forming a semiconductor device. Asemiconductor substrate is provided. A gate dielectric is formed overthe semiconductor substrate. A gate electrode is formed over the gatedielectric. A capping layer is formed over the gate electrode. An offsetspacer is formed over a sidewall of the gate electrode and the cappinglayer. A dopant is implanted in source and drain regions of thesemiconductor substrate adjacent to the offset spacer to form dopedsource and drain regions. A sidewall spacer is formed adjacent to theoffset spacer. A recess is formed in the semiconductor substrate in thesource and drain regions using a first etch process and a second etchprocess. The recess extends directly underneath the sidewall spacer apredetermined distance from a channel region. The predetermined distanceis determined by a thickness of the offset spacer. The first etchprocess is for removing a first portion of the recess adjacent to thesidewall spacer and the second etch process is for removing a secondportion of the recess directly underneath the sidewall spacer. Theforming the stressor material may further comprise providing one ofeither a tensile stress or a compressive stress on a channel region ofthe semiconductor device. The second etch process may be performedin-situ with forming the stressor material. The second etch process maybe performed using process gases selected from a group comprising HBr,SF₆, NF₃, Cl₂, O₂, Ar, and He.

Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under”and the like in the description and in the claims, if any, are used fordescriptive purposes and not necessarily for describing permanentrelative positions. It is understood that the terms so used areinterchangeable under appropriate circumstances such that theembodiments of the invention described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

Although the invention is described herein with reference to specificembodiments, various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. For example, the implant for changing the etchcharacteristic is described as being also useful as a source/draindopant that is not necessarily required. Because the area receiving theimplant is subsequently removed, it may be preferably to implant with adifferent element that causes a change in the etch characteristic. Otherexamples to consider for this include but are not limited to phosphorus,boron, oxygen, carbon, nitrogen, and boron difluoride. It may also bepreferable for the purpose of etch optimization for the implant to beself-amorphizing and to then leave the implanted region in an amorphousstate prior to performing the recess etch. Accordingly, thespecification and figures are to be regarded in an illustrative ratherthan a restrictive sense, and all such modifications are intended to beincluded within the scope of the present invention. Any benefits,advantages, or solutions to problems that are described herein withregard to specific embodiments are not intended to be construed as acritical, required, or essential feature or element of any or all theclaims.

Furthermore, the terms “a” or “an,” as used herein, are defined as oneor more than one. Also, the use of introductory phrases such as “atleast one” and “one or more” in the claims should not be construed toimply that the introduction of another claim element by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim element to inventions containing only one such element,even when the same claim includes the introductory phrases “one or more”or “at least one” and indefinite articles such as “a” or “an.” The sameholds true for the use of definite articles.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements.

1. A method for forming a semiconductor device comprising: providing asemiconductor substrate; forming a gate dielectric over thesemiconductor substrate; forming a gate electrode over the gatedielectric; forming an insulating layer over a sidewall of the gateelectrode; defining source and drain regions in the semiconductorsubstrate adjacent to the insulating layer; implanting a dopant in thesource and drain regions of the semiconductor substrate to form dopedsource and drain regions; forming a sidewall spacer adjacent to theinsulating layer and over a first portion of the source region and asecond portion of the drain region; anisotropically etching, in an etchchamber, the source and drain regions including the first and secondportions using a plasma etch with an active bias source; isotropicallyetching, in the etch chamber and after anisotropically etching, thesource and drain regions using an isotropic etch process achieved byturning off the bias source to form a first recess in the semiconductorsubstrate in the source region and a second recess in the semiconductorsubstrate in the drain region, wherein the first recess and the secondrecess extend underneath the sidewall spacer a predetermined distancefrom a channel region; and forming a stressor material in the firstrecess and the second recess including underneath the sidewall spacer.2. The method of claim 1, wherein implanting the dopant in the sourceand drain regions further comprises implanting one of arsenic,phosphorus, boron, oxygen, carbon, nitrogen, or boron difluoride in thesource and drain regions.
 3. The method of claim 1, wherein theanisotropically etching comprises using sulfur hexafluoride and whereinthe isotropically etching uses sulfur hexafluoride at a lowerconcentration than is used in the anisotropically etching.
 4. The methodof claim 1, wherein forming the stressor material in the recess furthercomprises epitaxially growing silicon carbon (SiC), silicon germanium(SiGe), or a combination of silicon, carbon, or germanium (SiGeC) in therecess.
 5. The method of claim 1, wherein forming the stressor materialin the recess comprises: growing a first stressor layer in the recess;and growing a second stressor layer over the first stressor layer. 6.The method of claim 1, wherein the anistropically etching comprisesusing hexafluoride and a carrier gas and the isotropically etchingcomprises using hexafluoride at a lower concentration than is used inthe anistropically etching and the carrier gas at a higher concentrationthan is used in the anistropically etching.
 7. The method of claim 6,wherein the isotropically etching is performed in-situ with forming thestressor material.
 8. The method of claim 6, wherein the second etchprocess is performed using process gases selected from a groupcomprising HBr, SF₆, NF₃, Cl₂, O2, Ar, and He.
 9. The method of claim 1wherein a thickness of the insulating layer determines the predetermineddistance.
 10. The method of claim 1, wherein forming the stressormaterial further comprises providing one of either a tensile stress or acompressive stress on the channel region of the semiconductor device.11. The method of claim 1, wherein forming the stressor material in therecess comprises: growing a first stressor layer with a first in-situdoping concentration; and growing a second stressor layer with a secondin-situ doping concentration over the first stressor layer.
 12. Themethod of claim 1, wherein forming a stressor material further comprisesgrowing the stressor material on exposed silicon in the recess.
 13. Themethod of claim 1, wherein forming a stressor material furthercomprises: growing the stressor material over the semiconductor device;selectively etching the stressor material from the gate electrode andthe sidewall spacer; and repeating the growing and etching apredetermined number of times.
 14. A method for forming a semiconductordevice comprising: providing a semiconductor substrate; forming a gatedielectric over the semiconductor substrate; forming a gate electrodeover the gate dielectric; forming a capping layer over the gateelectrode; forming an offset spacer over a sidewall of the gateelectrode and the capping layer; implanting a dopant to a first depth insource and drain regions of the semiconductor substrate adjacent to theoffset spacer to form doped source and drain regions; forming a sidewallspacer adjacent to the offset spacer so that portions of the dopedsource and drain regions are under the sidewall spacer; anisotropicallyetching, in an etch chamber, the semiconductor substrate to a seconddepth greater than the first depth in the source and drain regions inregions adjacent to the sidewall spacer, wherein the anistropicallyetching uses sulfur hexafluoride with an active bias source;isotropically etching, in the etch chamber with the bias source turnedoff, the portions of the doped regions of the semiconductor substrateunder the sidewall spacer using an etchant comprising sulfurhexafluoride that is selective between doped silicon and undopedsilicon; and forming a stressor material comprising a semiconductormaterial in the source and drain regions.
 15. The method of claim 14,wherein forming the stressor material further comprises forming one ofeither a first stressor material or a second stressor material in therecess, the first stressor material comprising silicon carbon (SiC) forproviding tensile stress for the channel region being of an N-channeltransistor, and the second stressor material comprising silicongermanium (SiGe) for providing compressive stress for the channel regionbeing of a P-channel transistor.
 16. The method of claim 15 wherein theisotropically etching is performed in-situ with forming the stressormaterial.
 17. A method for forming a semiconductor device comprising:providing a semiconductor substrate; forming a gate dielectric over thesemiconductor substrate; forming a gate electrode over the gatedielectric; forming a capping layer over the gate electrode; forming anoffset spacer over a sidewall of the gate electrode and the cappinglayer; implanting a dopant in source and drain regions of thesemiconductor substrate adjacent to the offset spacer to form dopedsource and drain regions; forming a sidewall spacer adjacent to theoffset spacer; forming a recess in the semiconductor substrate in thesource and drain regions using a first etch process performed in an etchchamber using an active bias source so that the first process isanisotropic and a second etch process performed in the etch chamber thatis isotropic resulting from turning off the bias source, the recessextending directly underneath the sidewall spacer a predetermineddistance from a channel region, the predetermined distance beingdetermined by a thickness of the offset spacer, wherein the first etchprocess removes a first portion of the semiconductor substrate adjacentto the sidewall spacer and the second etch process removes a secondportion of the semiconductor substrate, wherein the second portioncomprises portions of the doped source and drain regions underneath thesidewall spacer; and forming a stressor material in the recess, whereinthe stressor material comprises a semiconductor material of acomposition different from that of the semiconductor substrate.
 18. Themethod of claim 17, wherein forming the stressor material furthercomprises providing one of either a tensile stress or a compressivestress on a channel region of the semiconductor device.
 19. The methodof claim 17, wherein the second etch process is performed in-situ withforming the stressor material, and wherein the second etch process isperformed using process gases selected from a group comprising HBr, SF₆,NF₃, Cl₂, O₂, Ar, and He.